I am working on a swap to add a 9 inch rear (28 spline). I have a c4 transmission. Does anyone run this combo (I assume someone must) and if so, what driveshaft modification or replacement driveshaft was needed to accomodate the larger rear end. Also, does the vehicle being lowered 1 in. factor into this?
I would assume it bolts right up, at least I hope so because I am putting in the 9 inch next weekend. If anything it might require a different u joint but I doubt it.
The 9" pumpkin is deeper than the 8" (the yoke will be further towards the front of the car.) I've heard of people just using their stock driveshaft w/o modification, but its not recommended. You don't want to bend the driveshaft or break the tailhousing.
Measure to be sure, but if clearance isn't within spec, then you're asking for trouble unless the situation is addressed.
You might be able to find a driveshaft from a factory 9" Cougar with the appropriate transmission, but the usual solutions are having the original driveshaft shortened or using a shorter pinion yoke, such as from a Seventies vintage 1/2 ton pickup.
My understanding is that since the carrier is larger, there's no safe way. Also, is it easy to track down shorter yoke? Is there a measurement specification for it?
Having your driveshaft cut down to the proper length is a good way to go. You'll get the right length the first time, and you'll get your driveshaft rebalanced which is almost always a good thing.
I did the same thing. Went to a wrecking yard and found a 9" yoke that was about 1 1/2" shorter. Also had to buy (after much digging) a '69 Camaro 307 / Powerglide U joint yoke to adapt from the small block drive shaft to the larger u joint cap size on the 9" short yoke.
I took one and a quarter inch off mine. Make sure as others has stated to get you drive shaft rebalanced. the cut, balance, and new universal joints cost me $125.
Mine had a two piece shaft too. I was going to shorten it when my driveshaft guy recommended just making up a new one-piece unit in the length I needed. With heavy duty u-joints, it was right around $200.
I'm gonna need another one when I eventually swap in the AOD.
I Have Found That A 71-73 Shaft Is The Correct Length.
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